1. Field of the Invention
The present invention relates to driving device for driving optical components such as lens, and lens barrel comprising the driving device.
2. Description of the Related Art
As shown in Japanese Patent Publication No. 2005-148191, in a lens barrel such as interchangeable lens used for autofocusing single lens reflex camera, there exists a driving device for selectively driving focus lens group to two types of inputs. One of the two types of inputs is a driving force from a driving source such as vibration motor, which acts at automatic focusing, and the other is a driving force by user operation at manually focusing.
In order to transmit two types of inputs selectively, in a conventional driving device, an output ring is arranged, via a planetary roller, between an operation ring to which a driving force acted by user operation is transmitted and a driving ring to which a driving force is transmitted from a driving source such as a vibration motor. A lens housing which supports a lens via an engagement pin and a fork is connected to the output ring, by rotation of the output ring, the lens housing is movable to an optical axial direction.
A user sometimes turns too much an operating grip engaged to the operation ring. Therefore, a driving device has a constitution that faces between the operation ring and the planetary roller or between the driving ring and the planetary roller slip when the user further turns the operating grip after a lens housing has moved to an axial end portion of a movable area. This constitution results in transmitting no excessive force to the lens housing and preventing from breaking the lens housing and the engagement pin etc. Here, an outer circumference of the planetary ring can slip since the driving ring is fixed because of a holding torque between an elastic member and a rotor in the vibration motor.
The holding torque to fix the driving ring depends on a friction coefficient of the elastic member and the rotor in the vibration motor and a pressure force generated by a pressure member. Therefore, it is important to select a material or surface treatment for the elastic member and the rotor in the vibration motor in order to assure a certain level of the holding torque.
Further, it is necessary not to slip largely between the elastic member and the rotor when stopping the vibration motor. Also, it is necessary that the rotor rotates relatively in response to vibration of the elastic member when operating the vibration motor. Namely, in the vibration motor, it is important to select a material or surface treatment for the elastic member and the rotor of the vibration motor, which is difficult.